Obese couples may take longer to conceive

FRIDAY, Feb. 3, 2017 -- It's not just a woman's weight that matters when couples are trying to conceive, a new study suggests.

When a woman and her partner are both obese,
their chances for pregnancy during any menstrual cycle are about half
that of a normal-weight couple, according to the analysis from the U.S.
National Institutes of Health.

"It translates to maybe a longer time to get
pregnant," said lead study author Rajeshwari Sundaram. She is a senior
investigator at the U.S. National Institute of Child Health and Human
Development, a unit of NIH.

Prior studies show an association between
female obesity and reduced odds for pregnancy in a single menstrual
cycle, as well as a link between men's increased body weight and lower
sperm count, the researchers noted.

This study breaks new ground because it
enrolled couples hoping to get pregnant, not couples undergoing
fertility treatment. Measurements of body fat were taken before they
conceived, and the researchers followed each couple for a year or until a
pregnancy occurred.

Lauren Wise, professor of epidemiology at the
Boston University School of Public Health, said, "This study represents
an important contribution to the literature on couples' body size and
fertility."

Wise, who was not involved in the study, said
its strengths include use of more than one measure of body composition
and fertility over multiple menstrual cycles. The researchers also
controlled for physical activity, a key factor, she added. However, they
did not take couples' diets into account.

The findings, Sundaram said, are representative of reproductive-age couples in the United States.

A total of 501 couples from Michigan and Texas
joined the study from 2005 to 2009, as they were ready to try to get
pregnant. Infertile couples were excluded. The women ranged in age from
18 to 40 and the men were over 18.

The researchers interviewed each partner to
gather data on lifestyle, habits and medical and reproductive history.
Couples completed daily journals on lovemaking, and women recorded their
menstrual cycles and pregnancy test results.

Nurses weighed each participant and measured their height as well as their waist and hip circumference.

Height and weight were used to calculate body
mass index, an estimate of body fat. People with a BMI of 30 or higher
are considered obese. Researchers divided the obese couples into two
groups: BMIs of 30 to 34.9 and BMIs of 35 and over.

Overall, 27 percent of the women and 41
percent of the men were obese, the findings showed. In addition, the
majority of men and women engaged in physical activity less than once a
week.

It took couples with the highest BMIs (35 and
over) 55 percent longer to get pregnant compared with normal-weight
couples. When researchers accounted for other factors that might affect
fertility -- including age, smoking status, exercise and cholesterol
levels -- it took these obese couples 59 percent longer to get pregnant.

Larger women's waistlines -- roughly 35 or
more inches -- was also associated with longer time to achieve
pregnancy. But that finding didn't hold up when researchers adjusted for
other factors.

The study doesn't say why couples' obesity may
reduce their chances of conception. Sundaram said weight loss improves
many health outcomes. "And since it takes two to make a baby, it also
requires two to have a healthy weight," she reasoned.

The study can't prove a direct
cause-and-effect relationship. But the research team concluded that
couples' weight may be something that should be considered during
preconception counseling -- and not just to reduce their odds for type 2
diabetes, cancer and heart disease.

"A little weight loss from both of them should be beneficial for a quicker time to pregnancy," Sundaram said.

The study was published online Friday in the journal Human Reproduction.